Rena claims they make the quietest pumps, but you know how advertisers are. You have to take anything anyone who wants to sell your something with a grain of salt (or 2 or 3 or 53 grains...).
There are some tricks. Putting the pump on a folded towel, or putting it inside a folded up towel will help quiet it. The best trick is to have it suspended in the air. Some people tack a pair of pantyhose on the wall and put their pump in there. You may be able to use string to hang it from a table corner or something, too. The noise comes from the air pump vibrating against something, like the table. If you dampen the contact between a hard surface, like with the towel, or make it so that it doesn't touch anything, like suspeding it, there will be much less vibration and hence much less noise.
And yes, by all means, do not put the air pump in the tank. Firstly, you could electroctue yourself. Secondly, if the air pump is surrounded by water, how is it going to pump air?!?
